Tidal Constraints on Planetary Habitability

TL;DR

This paper reviews how tidal forces influence the habitability of terrestrial planets around low-mass stars, affecting orbital dynamics, rotation, obliquity, and internal heating, which may alter traditional habitable zone definitions.

Contribution

It introduces a comprehensive review of tidal effects on planetary habitability, proposing a revised habitable zone concept that accounts for tidal influences.

Findings

Tidal forces can cause orbital decay and circularization.

Tides influence planetary rotation rates and obliquity.

Internal heating from tides may impact habitability.

Abstract

We review how tides may impact the habitability of terrestrial-like planets. If such planets form around low-mass stars, then planets in the circumstellar habitable zone will be close enough to their host stars to experience strong tidal forces. We discuss 1) decay of semi-major axis, 2) circularization of eccentric orbits, 3) evolution toward zero obliquity, 4) fixed rotation rates (not necessarily synchronous), and 5) internal heating. We briefly describe these effects using the example of a 0.25 solar mass star with a 10 Earth-mass companion. We suggest that the concept of a habitable zone should be modified to include the effects of tides.